Many kinds of parenteral drug therapy require continuous delivery in preference to single or multiple injections. Benefits that accrue from continuous therapy may include, for instance, reduction of toxic or other side effects associated with sharp pulses of drug, significant improvement in the effectiveness of the therapy, and increased comfort of the patient. The traditional manner of administering sustained parenteral treatments is an intravenous drip. While this may be perfectly acceptable in a hospital environment, it obviously imposes severe restrictions on the activity of the recipient. As a result, considerable research over the last few years has been devoted to the development of small portable infusion pumps. A range of devices has appeared, including those with electric or clockwork motors that drive syringe or peristaltic pumps, and others powered by the elastic tension of an inflated balloon, or the vapor pressure of a volatile propellant. Literature incorporated herein by reference describing such pumps includes Controlled Release Micropump for Insulin Administration, (M. V. Sefton et al., Ann. Biomed. Eng., Vol 7, pp. 329-343, 1979), Continuous Intravenous Arabinosyl Cytosine Infusions Delivered by a New Portable Infusion System, (J. Bottino et al., Cancer, Vol. 43, pp. 2197-2201, 1979), or product brochures from Auto-Syringe, Inc., Hooksett, N.H. and Cormed, Inc., Medina, N.Y. These devices are typically strapped to the wearer, or carried on a belt or in a harness. Also, most are designed to deliver relatively large quantities of fluid and do not dispense small volumes of the order of a few milliliters or less effectively.
An alternative approach that has been exploited to a limited extent is to drive the infusor osmotically, using a Rose-Nelson pump activated by imbibition of water or other driving liquid. In comparison with mechanically driven devices, Rose-Nelson pumps are small, reliable, and simple and cheap to manufacture. U.S. Pat. No. 3,604,417 discloses a modification of the Rose-Nelson pump in which a moveable piston replaces the elastic diaphragm separating the drug and salt chamber, and both the drug and salt are loaded into the pump as solutions. U.S. Pat. No. 4,474,048 discloses another modification employing an impermeable elastic wall, and a moveable end wall which can be screwed in to deliver a pulse dose of the contained drug at any time during the operation of the pump. U.S. Pat. No. 4,474,575 is a variant of 4,474,048 where the flow rate of the dispensed agent can be varied by altering the area of semipermeable membrane exposed to the water chamber. U.S. Pat. No. 4,552,561 discloses a pump assembly for use with a small osmotic pump, which can be filled in advance of use with the active agent to be dispensed. The action of the pump is initiated by filling the lower chamber of the housing with a hydrogel. Once the pump is in action, an optional mechanism for delivering pulse doses can be employed. All these osmotic pumps are self driven and begin to operate as soon as they are primed with the contents of the several chambers. U.S. patent application No. 892,991 commonly owned with the present application and incorporated herein by reference in its entirety, describes a portable osmotic infusion pump that can be filled with the agent to be dispensed, the osmotic salt and the driving fluid, and then stored until required.
In developing a portable infusion device, there are patient compliance as well as technical problems to be addressed. For long term infusion therapy to be successful, the infusion device must be acceptable to the wearer. Devices that are bulky, heavy, uncomfortable or obtrusive, or that cause embarrassment, or otherwise limit the user's lifestyle, or that require complicated procedures to set up or monitor, are poorly accepted. Many of the devices described above, which typically weigh up to 1 lb, and have a base area of 10-20 square inches, suffer from these inherent problems. Even the smaller units have rigid housings, and are normally carried in a belt, cuff or vest. Thus there still exists a longstanding need for comfortable, compact, discreet devices that do not obtrude on the user's lifestyle or appearance.